Multi-stage centrifugal pumps are well known in the art and are generally comprised of a number of impellers which impart pressure and kinetic energy to a fluid which is being pumped and also includes a diffuser between impellers which guide the fluid to and from the impellers. An impeller and a diffuser comprises one "stage". Rotation of the impellers causes fluid to be pumped in one direction, e.g., upwardly and as it is pumped it develops a pressure differential which tends to force the impellers in a reverse direction, e.g. downward which is called "down thrust". These centrifugal pumps are widely used for submersible pumping of fluid from a well bore and in which the housing of the centrifugal pumps are cylindrical and are placed in a vertical position with the fluid entering the bottom of the pump and going out to the top. This "down thrust" is absorbed by bearings, located either externally or within each diffuser of the pump.
In one embodiment in order to transfer the thrust to an external bearing, the impellers are fixed axially to the shaft. This is commonly known as a "fixed impeller " pump. If the generated thrust is to be absorbed by a bearing in the stage itself, the impellers are not fixed axially to the shaft in order that each impeller may run on its individual thrust bearing. This type is commonly known as a "floating impeller pump". When pumping fluids from great depths, i.e., deep wells or against higher pressures, the "fixed impeller" pumps are at a disadvantage because of the limitation of the amount of thrust which can be transmitted down the shaft, or by the thrust capacity of the external bearing. When pumping fluids containing abrasive particles, such as sand, the "floating impeller" pumps are at a disadvantage because of the bearing wear due to these particles in the fluid. In situations where the pumps must deliver fluids containing abrasive particles from great depths, such as submersible oil field pumps, the pumps traditionally suffer extremely short lives. The use of bearing materials which are significantly harder than the abrasive in the "floating impeller" pumps have increased the pump life, but at an expense that is seldom justified.
It is therefore an object of the present invention to describe a multi-stage centrifugal pump having a novel means of transferring the down thrust from a plurality of impellers to a special bearing that is designed to operate in and be lubricated by the fluid being pumped.